Research on the nutrient regime in Lake Zapotlán (Mexico).

Nevado de Colima (extinct volcano) near Lake Zapotlán.

I have been conducting research on this lake since 2007. Lake Zapotlán is a small (1100 ha) endorheic lake in western Mexico that is an internationally recognized RAMSAR site. The Lake supports a fishery based on tilapia (Oreochromis aureus) and carp (Cyprinus carpio). Annual harvest of both is around 300 tonnes. Research has found that nutrients have increased in the Lake since 1994, and that there were significant seasonal differences in nutrient loads to the Lake over the 2007-2008 study period.  A preliminary P balance was constructed from available data showing that discharge from a wastewater treatment plant contributed over 30 tonnes of phosphorus annually to the Lake, resulting in growth of aquatic weeds - Typha latifolia (cattail) and Eichhornia crassipes (water hyacinth) - as well as phytoplankton blooms. The Lake also receives non-point sources P input from urban and agricultural runoff and from erosion and consequent deposition of sediment as a result of deforestation surrounding the Lake. 


Organized and participated in several lecture courses in Guadalajara, Mexico: “Environmental Management in Lakes and Estuaries”.

This series of lectures was directed at academics and government officials in the State of Jalisco. The objective of the courses was to transfer experience and knowledge of lake management in Canada to Mexico. The course built on my research experience working for the Canadian federal government as a scientist


Mercury concentrations in commercial fish in Lake Chapala (Mexico).

Previous studies, based on limited data, found elevated levels of mercury in carp in Lake Chapala, Mexico. The extent of mercury contamination in carp throughout the Lake had not been determined. In order to obtain reliable information about total mercury concentration in carp (Cyprinus carpio), 262 fish from 27 sites (approximately 10 fish per site) throughout the lake were analyzed. Results were expressed as the mean and median of the results at each site. Our results clearly show that: 1) with one exception, all the fish sampled were below the Mexican national standard of 1.0 ppm total mercury; 2) based on internationally recommended tolerances or reference doses, one can eat carp from Lake Chapala on a restricted basis; 3) mercury concentrations in carp decrease the farther away the sampled fish was from the mouth of the Lerma River; 4) further work needs to be carried out to confirm that the Lerma River is the major source of mercury to the lake; 5) one needs a large sample size from throughout the lake to produce reliable results with a low s.d. When one is studying a potentially contaminated fishery such as carp in Lake Chapala, it is important that the study be sound and that the results be irrefutable and interpreted carefully to avoid management agencies and the media misinterpreting the results causing unnecessary restrictions on fishing and consumption. This had been the case as a result of a previous study [Trasande, L.; Cortes, J.E.; Landrigan, P.; Abercrombie, L.M.; Bopp, R.F.; Cifuentes, E. Methylmercury exposure in a subsistence fish- ing community in Lake Chapala, Mexico: an ecological approach. Environ. Health 2010, 9, 1–10] where only 6 fish from a mrket had been samples.